SpeciationCh. 21

How Do Species Form?• Microevolution promotes

change in small population, when does enough change create a new separate species?

• Speciation process that forms new species from existing ones

• 2 forces isolate species:1) Geographic– Lead to reproductive isolation

2) Genetic– Pairing of chromosomes limit

mating, etc…

Categorizing Species• Linnaeus system Latin;

name made genius and species nomenclature– Base of morphological

species concept; connect species by physical traits

• What is the major problem with the morphological species concept?– Polymorphic species might

be confused as multiple species

– More exact methods of classification must be used

Modern Classification • Biological species concept

categorizes species on reproductive criteria– If members of two populations

cannot breed or produce fertile offspring under normal natural conditions they are not the same species

• If two population cannot exchange genetic information they are no longer connected

• How do we categorize asexual species?– Genetic markers through DNA

technology

Ancient Classification• How do we categorize

exist species?– Fossil records combined

with modern observations

• Phylogenetic species concept using morphological and genetic sequence data fossil records are grouped with similar existing species

Geographic Speciation• Populations of a species

spread across a wide range experience different environmental factors

• The greater the factors, the great genetic and phenotypic variation can be seen

• Subspecies variation in a species population that is easily categorized– Five subspecies of rat snake all

have different color patterns• Subspecies can still interbreed

when in contact

Ring Species• If two subspecies never come

directly in contact and never directly interbreed, are they still the same species?– Yes! They can be connected

through other subspecies• Ring species intermediate

between two populations that allows for the mixing of their genes– California salamanders

• Ring species may be showing the process of two separate populations finally dividing into two species

Reproductive Isolation Activity• YOUR TURN!!!• I’m done talking. Your turn to

teach each other.• Use the rest of the class and

tonight to research your topic in pairs

• Tomorrow we will form two groups (one member from each pair) and you will teach your topic to that group

• Prepare examples, bring in visual material, and be ready to answer their questions

• Here are the pairs and topics:

• Crystal and Donatello:• Explain ecological

isolation• Serena and Bruce:

• Explain temporal isolation

• Nick and Papaya: • Explain behavioral

isolation• Alex and Michael:

• Explain mechanical isolation

• Benjamin and Ezreal:• Explain gametic isolation

• Fox and Lyn:• Explain all postzygotic

mechanism

Types of Geographic Speciation 1) Allopatric Speciation

– “different homeland”– Physical barrier separates populations

• Two steps:1) Physically separate; stops gene flow2) Mutate over time to become reproductively isolated• Archipelagos are good examples; produce

species clusters close related species from a recent common ancestor; Darwin’s Finches

• Test speciation with second contact– Either groups are reproductively isolated or

they produce hybrids in hybrids zones– Over time these zones may disappear;

reinforcement

Types of Geographic Speciation 2) Parapatric Speciation

– “beside homeland”– Speciation between adjacent

populations; driven by hybrids having a lower fitness in the environment

3) Sympatric Speciation– “same homeland”– One population produces subgroups

that separate with time• Insect species lives on one type of

plant (host); a mutation in a part of the population causes a shift in the selected host

• New population moves to new host (host race); now separated they start their path towards speciation

• Polyploidy plants typically experience this type of speciation

Genes and Speciation • Genetic changes ultimately drive

speciation; all other factors just help in the eventual changes in the populations gene pools

1) Genetic Divergence genetic differences that reproductively isolate populations

• Swordtails and Platys hybrids produce lethal tumors; genetics wont let hybrids survive

• Snail species mutation reverse the direction shells coil, can no longer physically breed

• Sexual selection in birds changes in songs and dances make males of one population not attractive to females of another

Genes and Speciation 2) Polyploidy extra copies of chromosomes can reproductively isolate populations1) Autopolyploidy full

nondisjunction produces an unreduced gamete (diploid sex cell)– Grass, violets,

chrysanthemums– Unreduced gametes mix to

make tetraploid offspring– Can self-pollinate or mate

with other tetraploid plants– Reproductively isolated

from all non-polyploidy populations

Genes and Speciation 2) Polyploidy extra copies of chromosomes can reproductively isolate populations2) Allopolyploidy two closely related species form a hybrid, which is normally sterile, BUT if self-fertilize after forming gametes through meiosis or gains the needed chromosomes, it can form a new species

– Coffee, cotton, potatoes, tobacco

– Very fast speciation

Genes and Speciation 3) Chromosome Alteration inversions, translocations, deletions, and duplications can all alter the genome enough to cause speciation

– Humans (46) diverged from gorillas and chimps (48) possibly because we lost 2 chromosomes that fused into Chromosome #2

– Inversion at centromere on #2 also points to divergence between chimps/humans and gorillas/orangutans

– Humans differ from chimps by 6 other inversions

Homework• Suggested Homework:

– Test Your Knowledge Ch 21

• Actual Homework (Wednesday):– Discuss the Concepts #3– Interpret the Data– Apply Evolutionary

Concepts• Homework for Tuesday’s

class:– Summary of each type of

reproductive isolation with examples

– Be prepared to do the group sharing again with 22.1 and 22.2

• Crystal and Donatello:• Explain conditions for making

fossils/why so few fossils survive• Serena and Bruce:

• Explain relative and absolute dating of fossils

• Nick and Papaya: • Explain how we use fossils to map

out life millions of years ago• Alex and Michael:

• Explain the continental drift and how it effects speciation

• Benjamin and Ezreal:• Explain slow gradual changes to the

surface of the Earth• Fox and Lyn:

• Explain sudden dramatic changes to the surface of the Earth